1. Field of the Invention
This invention related to surfactant concentrates containing ester sulfonates and to their use in domestic and industrial cleaning preparations.
2. Description of Related Art
In industrial processes, .alpha.-sulfofatty acid ester salts are obtained in the form of aqueous pastes by neutralization of .alpha.-sulfofatty acid esters with aqueous alkail hydroxide. The starting materials used in these processes are fats and/or oils of natural origin which are obtained by ester cleavage and subsequent esterification with lower alkanols, particularly methanol, or by transesterification of natural triglycerides with lower alkanols. The fatty acid ester mixtures formed contain fatty acids in which the length of the alkyl chains covers a comparatively broad range, depending on the origin of the natural starting material. C.sub.10 -C.sub.24 fatty acids are normally used. Tallow or palm oil are preferred as natural starting materials.
The sulfonation of the fatty acid ester mixtures with gaseous SO.sub.3 leads to more or less heavily discolored acidic crude sulfonates which have to be bleached and converted into ester sulfonate pastes by neutralization to a pH-value of from about 6 to 7. Pastes such as these are acquiring increasing practical significance as surface-active agents or wetting agents for detergents and cleaning preparations which may be prepared from natural raw materials.
Pastes of alkail metal salts of .alpha.-sulfonated fatty acid alkyl esters (also known as "ester sulfonate salts") are difficult to handle on an industrial scale insofar as they show unusual concentration/viscosity behavior. It is only in comparatively low solids concentrations in water, for example, up to solids contents of around 35% by weight, that solutions or suspensions such as these can be stirred or transported and pumped sufficiently well without interfering with the course of industrial processes. "Pumpable" products are generally understood to be products which have a viscosity below 10,000 mPas at a temperature of around 70.degree. C. Higher solids contents (above about 40% by weight) in solutions or suspension of ester sulfonate salts lead to a disproportionately high increase in viscosity so that the mixtures can no longer be said to be free-flowing and pumpable. This gives rise to several major disadvantages. Highly concentrated ester sulfonate salt pastes cannot be directly neutralized by neutralization of the crude sulfonic acid mixture with aqueous alkail metla hydroxide solution because the fluidity and hence the uniform mixing of the components of the neutralization reaction is no longer guaranteed. In addition, it is not possible on an industrial scale to dissipate the heat of the neutralization reaction to the necessary extent. The resulting increase in both the concentration and the reaction temperature produces undesirable secondary reactions, including in particular an undesirably high formation of disalts of the .alpha.-sulfofatty acid with ester cleavage. In addition, it may be regarded as a disadvantage that, in view of the increase in viscosity, the ester sulfonate pastes obtained can no longer be pumped off or transported through pipelines on an industrial scale. The pipelines become blocked so that the operation of the plant as a whole is interrupted for prolonged periods.
Heretofore, numerous proposals have been put forward with a view to improving the situation. Thus, German Application 33 05 430 proposes the addition of long-chain, optionally substituted alcohols as viscosity regulators. This enables the viscosity to be reduced to below the desired level of 10,000 mPas at 70.degree. C.
According to German Application 33 34 517, aqueous suspensions of .alpha.-sulfofatty acid ester salts are said to be sufficiently fluid after an addition of lower alcohol sulfates and lower alcohols. The aforementioned viscosity-reducing compounds are initially introduced into the reaction mixtures in higher concentrations than ultimately necessary, and then removed by concentration.
According to German Application 31 23 681, a highly concentrated aqueous solution of an .alpha.-sulfofatty acid ester salt is prepared by initially neutralizing the crude sulfonic acid to a pH-value of from 2.5 to 4 with caustic alkali metal solution in the presence of a lower alcohol and then bringing the pH-value to the necessary level of 6 to 7 by addition of more alkali metal solution in a second neutralization step.
The known proposals mentioned above all relate to the usual industrial starting materials, i.e., fatty acids of natural origin in which the alkyl groups in the natural fatty acid mixture cover a comparatively broad chain-length range, e.g., from C.sub.10 to C.sub.24. With a narrower chain-length range of the alkyl group in the natural fatty acids, for example from C.sub.16 to C.sub.18, as obtained for example in the splitting of tailow or in the working up of palm oil, the measures to lower viscosity may be distinctly reduced. This is the subject of German patent application P 34 39 520.0, according to which aqueous pastes of ester sulfonate salts prepared from C.sub.16 -C.sub.18 fatty acids have solids contents of at least 60% by weight and are pumpable at 60.degree. C. although they are substantially free from viscosity regulators. However, ester sulfonate salt pastes of this type are attended by the disadvantage that, as stated in German patent application 34 39 520.2, they have comparatively high contents of "disalt", i.e. disalts of a .alpha.-sulfofatty acid, which are formed with cleavage of the ester in the strongly alkaline medium. Disalts such as these, which may make up as much as 25% by weight of technical degree .alpha.-sulfofatty ester salts are highly undesirable as a secondary product because they seriously impair the flow properties of the pastes. Accordingly, a "disalt" content below 25% by weight is desirable for high-quality ester sulfonate pastes.
An object of the present invention is to provide alkali metal salts of .alpha.-sulfonated fatty acid alkyl esters in a form in which they are fluid and pumpable at low temperature, i.e., alkali metal salts thereof having a viscosity below about 10,000 mPas. The ester sulfonate salts herein are to be made available with high active-substance contents, i.e. contents of surfactants of distinctly greater than 50% are to be obtained in the concentrates.